Conventional seat reclining devices for inclining a seat back at the desired angle include, for example, the one disclosed in Utility Model Publication of Unexamined Application No. SHO-59-41153. As shown in FIG. 5, this device includes a base plate 101 which is attached to the seat cusion A, an arm 103 which is fixed to the seat back B which is rotatably attached on the outside of this base plate 101, an upper tooth 105 which is attached to this arm 103, a lower tooth 107 which meshes with this upper tooth 105 and holds the arm 103 at the desired angle of rotation, and release control section 109 which can engage and disengage this lower tooth 107 to and from the said upper tooth 105. The arm 103 is gripped between the base plate 101 and a holder plate 111 and is attached to the base plate 101 through an arm shaft 113. On the other side of the holder plate 111, the release control section 109 is attached to the arm shaft 113 through an E-ring 115. Then, on the outside of that, a return spring 119 is attached respectively to the base plate 101 along the same axis to the arm 103 through a washer 117. Further, the upper tooth 105 is normally meshed with the lower tooth 107. This lower tooth 107 is attached between the base plate 101 and the holder plate 111 by a pin 121. A cam 125 is coupled to a depression 123 in the lower tooth 107. This cam 125 is attached between the base plate 101 and the holder plate 111 through a shaft 127. On the outside of the holder plate 111, a rod lever 129 is fixed and coupled to the shaft 127. A pin rod 131 is formed in the other end of the rod lever 129. The pin rod 131 is inserted into the long hole 133 in the lever control section 109, and thus the rod lever 129 is also coupled to the section 109. It is axially fixed in place by a nut 135 which prevents it from pulling out.
In such a seat reclining device, in order to adjust the seat back B to the desired angle, the lower tooth 107 and the upper tooth 105 are disengaged through the cam 125 which is controlled by the release control section 109. Next, after the seat back B has been rotated to the desired angle, it is held in a desired inclination attitude by engaging the upper tooth 105 with the lower tooth 107.
The tooth sections a and b of the upper tooth 105 and the lower tooth 107 must be strong enough to withstand the forces applied to the seat back B during, for example, a vehicle collision. For this purpose, the toothed sections a and b of the upper tooth 105 and the lower tooth 107 are finished to high accuracy with specified standard pitch.
The final adjustment to the angle at which the seat back will be held is determined by the pitch of the tooth section a formed in the upper tooth 105. If it is desired to have a finer adjustment, so that the rotating angle is made smaller, the pitch of the tooth section a must be smaller. If the pitch of the toothed section a is made smaller than the standard pitch, the strength can be adversely affected.
The purpose of this invention is to provide a seat reclining device in which secure meshing is possible and fine adjustment of the seat back angle is possible while maintaining the same strength as in the conventional device.
Another existing type of seat reclining device is disclosed by Japanese Utility Model Application No. SHO-59-10186. This will be explained with reference to FIG. 10. The seat reclining device R comprises a base plate 10 which is fixed to the seat cushion A, an arm 11 is fixed to the seat back B which is pivotally attached on the outside of this base plate 10, an upper tooth 11a which is formed in this arm 11, a lower tooth 18 which meshes with this upper tooth 11a and holds the arm 11 at the desired angle of rotation, and a release lever 13 which can be engaged this lower tooth 18 to and disengaged from the said upper tooth 11a. The said arm 11 is gripped between the base plate 10 and a holder plate 14, and is attached to the base plate 10 through an arm shaft 12. On the outside of the said holder plate 14, a release lever 13 is attached to the said arm shaft 12 through the E-ring 15. To the outside of it, in turn, a return spring 17 is attached to the base plate 12 along the same axis as the arm 11 through a washer 16. In addition, the upper tooth 11a which is solidly attached to the arm 11 is normally engaged to the lower tooth 18. This lower tooth 18 is attached between the base plate 10 and the holder plate 14. A cam 20 is engaged to a depression 18b in the lower tooth 18. This cam 20 is attached between the base plate 10 and the holder plate 14 through the shaft 21. In addition, a rod lever 22 is fixed and coupled to the shaft 21 on the outside of the holder plate 14. A pin rod 22a is formed in the other end of this rod lever 22. The pin rod 22a is inserted into the long hole 13a in the lever 13, and the rod lever 22 is thus coupled to the lever 13. It is fixed in place by a push nut 23 which prevents it from pulling out.
In a seat reclining device with the above configuration, in order to keep the lower tooth and the upper tooth securely engaged and provide the strength needed to withstand, for example, a vehicle collision, the toothed sections of the upper tooth and lower tooth are finished to high precision by a process such as broaching with an appropriate standard pitch. In such meshing of an upper tooth with a lower tooth, in order to provide finer adjustment of the seat back reclining angle, the pitch of the toothed sections of the upper tooth and the lower tooth must be made smaller, but in this case there are limits from the points of view of both strength and precision. In addition, in this kind of seat reclining device, the release lever and the lower tooth are coupled through a rod lever and a cam, so that when the seat back is pushed down in the forward direction, the release lever is pulled up from its usual position and there is a danger that the seat belt mounted to the seat position will get caught between the release lever and the seat cushion. If the seat belt is buckled up around a rider while it is caught between the release lever and the seat cushion, there is a danger that while the car is moving the release lever will pop up and the seat back will fall forward, which is dangerous.
This invention focuses on problems such as those described above. Its purpose is to provide a seat reclining device in which the upper tooth and the lower tooth are kept securely engaged, the strength is adequate, and in addition the seat reclining angle can be more finely adjusted than has been the case previously.